A medical examination performed in a hospital needs to collect blood or tissue from chronic illness patients and thus has disadvantages of putting the patients to a lot of inconvenience. Recently, there have been continued researches on a noninvasive method of diagnosing diseases, for example, chronic obstructive pulmonary disease (COPD), asthma, pulmonary tuberculosis, lung cancer, diabetes, etc. based on a human-body respiratory gas analysis.
An optical gas sensor has been employed in analyzing a spectrum and diagnosing chronic diseases on the principle that various respiratory gases, for example, nitrogen monoxide (NO), carbon monoxide (CO), acetone or the like gas which reflects a human body's physical conditions are different in wavelength of light absorbed therein while transmitting the light.
There has been disclosed an optical gas sensor (US 2013/0081447), in which a hollow optical waveguide having a diameter of about 2 mm is manufactured as folded or twisted to get a long optical path within a small space, and components of gas are detected by transmitting light through the optical waveguide internally filled with the gas to be sensed.
Such a conventional optical gas sensor additionally needs a pump for inhaling and exhausting the respiratory gas in a small and complicated optical waveguide, and thus has a limit to miniaturization and a complicated structure.